Geographical Structuring in the mtDNA of Italians

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 92; no. 20; pp. 9171 - 9175
• Main Authors: Barbujani, Guido, Bertorelle, Giorgio, Capitani, Giulia, Scozzari, Rosaria
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 26.09.1995; National Acad Sciences; National Academy of Sciences
• Subjects: Autocorrelation; Biological Evolution; Demography; Deoxyribonucleic acid; DNA; DNA, Mitochondrial - genetics; European Continental Ancestry Group - genetics; Evolution; Evolutionary genetics; Genetic diversity; Genetic Variation; Geography; Haplotypes; Humans; Italy; Mathematics; Mitochondrial DNA; Models, Genetic; Polymorphism, Restriction Fragment Length; Population genetics; Population growth; Restriction Mapping; Italy
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.92.20.9171

Geographical patterns of mtDNA variation were studied in 12 Italian samples (1072 individuals) by two different spatial autocorrelation methods. Separate analyses of the frequencies of 12 restriction morphs show North-South clines, differences between Sardinia and the mainland populations, and the effects of isolation by distance. A recently developed autocorrelation statistic summarizing molecular similarity at all sites (AIDA; autocorrelation index for DNA analysis) confirms the presence of a clinal pattern; differences between random pairs of haplotypes tend to increase with their geographical distance. The partition of gene diversity, however, reveals that most variability occurs within populations, whereas differences between populations are minor (GST= 0.057). When the data from the 12 samples are pooled, two descriptors of genetic variability (number of polymorphic sites and average sequence difference between pairs of individuals) do not behave as expected under neutrality. The presence of clinal patterns, Tajima's tests, and a simulation experiment agree in suggesting that population sizes increased rapidly in Italy and Sicily but not necessarily so in Sardinia. The distribution of pairwise sequence differences in the Italian peninsula (excluding Sardinia) permits a tentative location of the demographic increase between 8000 and 20,500 years ago. These dates are consistent with archaeological estimates of two distinct expansion processes, occurring, respectively, in the Neolithic and after the last glacial maximum in the Paleolithic. Conversely, there is no genetic evidence that such processes have had a major impact on the Sardinian population.